John Rain series could be really good and are written in a way that would be relatively easy to adapt.
A fantasy series I've always loved since a kid was the Elric of Melnibone series by Michael Morcock. That or the Corum series. Either would be completely badass, but would have to be done well or it would be just another cheesy fantasy movie.
I like many of your suggestions, but cringe at the expectation some of you seem to have that the movies be true to book. In my opinion, the best adaptations of books are ones that capture the themes and the broad strokes, but aren't bound to address every detail.
For example, One Flew Over The Cuckoo's Nest was a fantastic book, and Jack Nicholson's movie was equally fantastic even though many of the details had been changed.
If anything, the Harry Potter books suffered from the burden of being too true to the books. Honestly, every one of the movies was bloated and overly long, but it was clear that the director tried to pack too much in. LOTR trilogy was the same way, and I've read the books several times over the years. I mean, really... at times it went from being a New Zealand tourist movie to gay, softcore, hobbit porn, to just being a very slow, boring homage to classic fantasy novels.
Thomas Covenant the Unbeliever could be really, really good, but they'd have a hard time marketing movies in which the main character is so unlikable an anti-hero that he doesn't truly redeem himself until well into the final chapter. It's been decades since I read those books, and I truly loved them at the time, but I remember him being kind of a jerk throughout the entire series.
Ender's Game would be AWESOME. Finding a group of young kids who could play those geniuses would be a real challenge.
F Paul Wilson wrote some great books. Actually, I wouldn't mind seeing The Touch as a movie, either. That would be cool.
Ultimately, if nothing else, you guys are reminding me of novels I read long ago that I loved but haven't really thought about in years. Thanks for that!!!